Security devices

Abstract

A sheet element, such as a banknote, having an authenticating device in the form of a strip extending across the sheet and having at least one edge provided with a non-rectilinear portion or portions providing difficulty in copying for the forger and preferably shaped to provide coded information relating to the sheet element. In the case of a banknote, one or both edges of the strip may have wavy-shaped portion or portions, of which characteristics such as amplitude and periodicity can be employed to encode such information as the issuing authority, currency, denomination and serial number. Other aspects of the invention concern a method of verification comprising providing a sheet element as above and sensing the non-rectilinear edge or edges to derive the coded information, and a method of slitting a sheet comprising operating a slitting assembly to slit the sheet along a number of slitting lines into a plurality of strips as aforesaid.

I claim: 
     
       1. A currency document comprising a sheet element bearing thereon legible information and incorporating authenticating means in the form of a visible thin strip, said strip having along at least a portion of one edge of a width dimension of said strip a wave-form variation, said variation defining coded information relating to the document. 
     
     
       2. A document according to claims 1 wherein one edge of said strip is rectilinear. 
     
     
       3. A document according to claim 1 wherein said portion of said strip having said wave-form variation has a non-uniform width. 
     
     
       4. A document according to claim 1 wherein said portion of said strip having said wave-form variation is of substantially uniform width. 
     
     
       5. A document according to claim 1 wherein said edge of said strip includes said wave-form variation along its whole length. 
     
     
       6. A document according to claim 5 wherein the wave-form variation on said portion of one edge is of a different periodicity and/or amplitude to the wave-form variation on said portion of the other edge of said strip. 
     
     
       7. A document according to claim 5 wherein said wave-form variation of said edge follows a regular oscillatory path. 
     
     
       8. A document according to claim 7 wherein the wave-form variation on said portion of one edge is on the same periodicity and amplitude as the wave-form variation on said portion of the other edge of said strip. 
     
     
       9. A document according to claim 1 wherein said edge is formed with a plurality of wave-form variations with rectilinear portions there between. 
     
     
       10. A document according to claim 1 wherein additional coded information in the form of apertures is provided.